Miniaturized electronic imaging chip

ABSTRACT

A miniaturized electronic imaging chip has stratified layers wherein a base silicon layer has a peripheral edge defining an area and a thickness which allows passage therethrough of most UV, visible and IR light. A pixel layer is formed on the back side of this first silicon layer. At least one interconnect layer is bonded to the pixel layer. Electric leads are bump bonded to the bonding pads on the outermost interconnect layer and extend away from it within the area for attachment to means for sensing electrical signals generated by an image projected onto the pixel layer through the silicon layer. Preferably, the leads are perpendicular to the chip. A unique method of manufacturing the miniaturized electronic imaging chip from a standard CCD, having a peripheral edge defining a first area, comprises the steps of shaving a silicon substrate, having a peripheral edge defining a second area which is smaller than the first area, on the back side of the standard CCD to a thickness which allows passage of a light image therethrough. The CCD then is reversed so that the image is projected through the thinner back side of the silicon substrate. Leads are bumped bonded to the former front surface of the CCD within the smaller second area for supplying electrical signals to and from the CCD.

This application is a continuation-in-part of my application U.S. Ser.No. 954,550, filed Sep. 30, 1992, now abandoned.

TECHNICAL FIELD

This invention relates to an electronic imaging chip and particularly toa method of modifying the architecture of a standard electronic chip tocreate a new miniaturized chip with enhanced capabilities.

BACKGROUND ART

Although electronic imaging chips, such as CCDs, have found extensiveuse in electronic imaging devices, their utilization in endoscopes hasbeen limited because of size. The trend is to make endoscopes of everdecreasing diameter so as to be less intrusive when introduced into thebody of a patient. However, the ability to reduce the diameter of theendoscope is often controlled by the size of the imaging device. Thestandard CCDs do not allow for miniaturization in their presentconfiguration. Because of their relatively large size, stereoscopicimaging, especially, has not been possible in a small endoscope. Inorder to overcome the relatively large size of the CCD they have oftenbeen positioned longitudinally within the endoscope and used either forside viewing or in combination with a prism to provide end viewing, allof which adds to the complexity, weight, cost and ultimate size.

Examples of attempts to compensate for the large sized standard CCDs instereoscopic endoscopes are illustrated in a number of patents.

Tasaki et al., U.S. Pat. No. 3,520,587, discloses a stereoscopicendoscope having two flexible fiber optic systems with objective lenssystems being located at the distal end of each for focusing an image ofthe site to be inspected. An ocular is located at the proximal end ofeach fiber bundle for viewing the transmitted images. A visualperception in three-dimension is thereby created. This device isintended to provide a stereoscopic endoscope of limited diameter, butbecause of the use of light fibers for both transmitting and receivinglight and the requirement for relatively sophisticated electronics, thedevice is still larger than desired for many applications and is quitecostly.

Yabe, U.S. Pat. No. 4,786,965, discloses a conventional electronic chipstructure in which a base plate is positioned behind the chip. This baseplate as an extended side portion to which the leads on the chip areconnected. This requires the endoscope to be of sufficient diameter toaccommodate the extended side portion. Light is not transmitted throughthe base and it has no light transmitting qualities.

Miyazaki, U.S. Pat. No. 4,926,257, discloses a stereoscopic endoscopecomprising a single solid-state image sensor and an optical imagesystem. Stereoscopic imaging is made possible by shifting thesolid-state image sensor back and forth between the two optical imagingsystems. A prism system is provided in which images are sequentiallytransmitted to provide the three-dimensional image for viewing.

Jones, Jr. et al., U.S. Pat. No. 4,924,853, also discloses astereoscopic endoscope using a single imaging lens whereby the image issplit by a split beam prism, which images are converted to electricalsignals and displayed on a television screen. The images are transmittedfrom the lens by means of coherent light transmitting elements. Thisdevice also provides for the alternate transmission of images to providea three-dimensional image for viewing.

Yajima et al., U.S. Pat. No. 4,862,873, discloses a stereoscopicendoscope comprising a pair of optical guides which are capable ofconducting and illuminating light to be reflected on the site to beobserved. While one optical guide conducts the illuminating light, theother optical guide conducts the light from the object being observed.The optical guides can be switched from one function to the other,thereby creating a stereoscopic image.

Tsujiuchi et al., U.S. Pat. No. 4,895,431, discloses a stereoscopicendoscope in which a first endoscope image is taken at one positionwhile a second endoscopic image is taken from a second position. Theendoscopic images are partially overlapped with means for detecting therelationship between the first and second images, thereby providing athree-dimensional image.

DISCLOSURE OF THE INVENTION

In accordance with this invention a miniaturized electronic imaging chipis provided which is of the interline transfer architecture. This devicecomprises stratified layers wherein a base silicon layer is thin enoughto allow passage therethrough of most UV, visible and IR light whichstrikes a pixel layer formed on the back side of the base silicon layer.Various interconnect layers including an interlace circuit, verticalshift register, horizontal shift register and an output register areterminated on the chip margins on the surface of the outermostinterconnect layer as bonding site pads to allow bump bonding ofelectrical pins extending away from the chip for attachment to means forsensing electrical signals generated by an image projected onto thepixel layer through the base silicon layer. Preferably, the leads arebonded perpendicular to the chip surface and lie within an area definedby the peripheral edge of the silicon layer.

A unique method of manufacturing the miniaturized charged-coupled devicecomprises the steps of shaving a silicon layer to a sufficient thinnessto allow passage of a light image therethrough. The CCD is then reversedso that the image is projected through the shaved silicon layer. Leadsare bumped bonded to the former front surface of the CCD inperpendicular relation thereto so as to lie within the area defined bythe peripheral edge thereof for supplying electrical signals to and fromthe CCD. These modifications significantly reduce the outside dimensionsof the CCD architecture by totally eliminating the substrate whichsupports the CCD and holds the standard electrical leads and requiredpackaging.

By this method, a CCD is provided whose surface area is no greater thanthat defined by the pixel layer itself. Furthermore, the total thicknessof the chip is reduced. This makes the chip sufficiently small to beused in stereoscopic endoscopes and in endoscopes of very smalldiameter.

Additional advantages of this invention will become apparent from thedescription which follows, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a prior art CCD supported in an openingin a large substrate which includes the electronic packaging;

FIG. 2 is an exploded, diagrammatical, enlarged view of the CCD of FIG.1;

FIG. 3 is an exploded, diagrammatical view of a CCD constructed inaccordance with this invention;

FIG. 4 is a section showing the CCD of FIG. 3 used with a lens system inan endoscope; and

FIG. 5 is a sectional view showing the architecture of a CCD constructedin accordance with this invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with this invention, a method has been provided formodifying the architecture of an electronic imaging chip tosubstantially reduce its size and increase its capabilities. The term"imaging chip" as used herein is intended to include any of a wide rangeof photosensitive chips used for imaging, such as CCDs, CIDs, CPDs andMOSs. The discussion which follows will be directed specifically to aCCD chip, but it will be understood that the invention is equallyapplicable to the other above-mentioned chips.

FIGS. 1 and 2 show a conventional electronic chip C. The chip includesone or more interconnect layers, such as layer 10, having a peripheraledge 11, and layer 12, having a peripheral edge 13, through which animage is projected onto a pixel layer 14, having a peripheral edge 15.This layer is supported on a thick silicon base layer 16, having aperipheral edge 21 sized to just fit within and be mounted in an opening17 in a large substrate 18, having a peripheral edge 19 which defines afirst area. The substrate 18 is similar to a picture frame whichprovides a support for the chip and protects it from damage. Thissubstrate may be made of any one of several materials, such as ceramicor plastic. A plurality of leads 20 connect the CCD in interconnectinglayers to electrical contacts 22 on substrate 18. Electrical pins 24 areconnected to the substrate and to electrical contacts 22, along themargins, as shown, for connection to electrical wires (not shown) fortransmitting electrical information into and out of the chip. It will benoted that the images projected in the direction of arrow 26 shown inFIG. 1, must be projected through interconnect layers 10 and 12 ontopixel layer 14 thereby reducing the amount of light that can betransmitted to the pixel layer. The light which does pass through theinterconnect layers is distorted by them, resulting in a distorted imagebeing projected onto the pixel layer. Also, since substrate 18 issubstantially bigger in area than pixel layer 14, a significantly largerarea is required by the chip than the area occupied by the pixel layerand the associated layers above and below it.

By the method of the present invention, an improved chip of the typeshown in FIGS. 3 and 4 is provided. In this regard, the chip C isremoved from substrate 18 and turned over so that silicon layer 16 is atthe top. Next, silicon layer 16 is shaved down to a sufficiently thinthickness to allow the transmission of a light image. The desiredthickness will vary depending on the particular application. Anacceptable thickness range has been found to be between 3 and 200microns. A preferred range is between 6 and 10 microns. After shaving, athin layer 30 is formed, having a peripheral edge 31 defining a secondarea, which is smaller than the first area defined by peripheral edge19. After reversing the chip, interconnect layers 10 and 12 are mountedbelow pixel layer 14, as shown, and posts 32 are indium bump bonded tointerconnect layer 10 and extend generally perpendicular thereto withinthe second area to provide electrical connections for bringing data intoand out of the chip. Advantageously, the posts are positioned within thearea defined by peripheral edge 15 of pixel layer 14, With thisarrangement, the area of modified chip C' is no larger than the area ofpixel layer 14, such as 2 mm square.

This allows the modified chip C' to be placed inside an endoscope 34having a diameter no larger than 3 or 4 mm. The chip is shown near thedistal end of endoscope 34, as shown in FIG. 4, with an appropriate lenssystem 36 for focusing an image on the chip. Because of the thinness ofsilicon layer 30 and the fact that the light does not need to passthrough the interconnect layers 10 and 12, it is possible for pixellayer 14 to receive up to 90% of UV or infrared light in addition tolight in the visible light range. Thus, the use of the chip is enhancedfor a wider light spectrum thereby increasing its utility. In someapplications, filters can be placed over the chip to regulate thefrequency of light being utilized by the CCD. In addition, since thelight does not have to pass through the interconnect layers, there isless distortion of the image as it is projected onto the pixel layer.Also, a chip constructed in the manner of chip C' can be autoclavedwhereas the conventional chip and packaging will be damaged or destroyedby the high temperatures required for autoclaving. Because of theminiaturization of chip C', a pair of such chips can be used inside-by-side relationship within a stereoscopic endoscope withoutresulting in an endoscope of excessively large diameter. Also, they canbe used alone to provide a very miniaturized endoscope, as discussedabove, for use in passageways and through trochars in a less intrusivemanner than that which was previously possible.

In the foregoing description the pixel layer and interconnect layershave been described as being separate distinct layers. In reality, theelements that make up the chip are stratified, as shown in FIG. 5 and asis well understood by those skilled in the art of the construction ofCCDs. Therefore, the term "layers" as used herein is intended to coverthe pixel layer and interconnect layers in the more integrated andstratified arrangement shown in FIG. 5.

This invention has been described in detail with reference to aparticular embodiment thereof, but it will be understood that variousother modifications can be effected within the spirit and scope of thisinvention.

I claim:
 1. A miniaturized electronic imaging chip comprising:agenerally rectangular silicon base layer having a thickness which allowsa light image to pass therethrough, said silicon layer having a firstside, through which the image is projected, and a second side; a pixellayer having a first and second side, said first side of said pixellayer being attached to said second side of said silicon layer, saidpixel layer further having a peripheral edge; at least one interconnectlayer bonded to said second side of said pixel layer; and electricalleads bonded to and extending substantially perpendicular from saidinterconnect layer and within an area defined by said peripheral edge ofsaid pixel layer for attachment to means for transmitting electricalsignals to and from said pixel layer.
 2. Apparatus, as claimed in claim1, wherein:said silicon layer as a thickness between 3 and 200 microns.3. Apparatus, as claimed in claim 1, wherein:said silicon layer has athickness between 6 and 10 microns.
 4. Apparatus, as claimed in claim 1,wherein:said electrical leads are indium bump bonded leads. 5.Apparatus, as claimed in claim 1, wherein:said silicon layer has lighttransmitting qualities which allow passage of UV, visible and IR lighttherethrough.